Dr. David Newberg has found that human milk inhibits the binding of gp120, the HIV envelope glycoprotein, to the human host cell receptor, CD4, This inhibitor activity apparently protects the suckling infant against transmission of the virus from the mother. The inhibitory material is a macromolecule that is larger than 250 kDa and appears to be either sulfated or glycosylated. It is proposed that the HIV inhibitory factor(s) in human milk be purified and its biochemical, immunological and biophysical characteristics be defined. In addition Dr. Newberg will try to determine the structure of the active inhibitory factor(s) using standard chemical and enzymatic degradation methods followed by mass spectrometry analyses that will include MALDI, ESI, and LSIMS for molecular weights and LSIMS/MS and ESIMS/MS for structural details.